Thanks for all the suggestions as to why the rear end was breaking on right hand turns in the final.

Got it home and the C-Drive blade from the left hand rear out drive had disappeared meaning one wheel had around 1mm of play either way. So I guess when he lifted off, that wheel lost grip/drive for a fraction of a section has it dropped back.

Couldn't see anything else wrong - and as it started playing up suddenly rather than progressively, I guess that could be it?

Will also take some grip off the front as well to see if that helps and see if I can redo the topdeck suspension mounts to get a bit more camber in - can only get 1.5-2mm at the moment.